1. Field of the Invention
The present invention relates to a honeycomb filter and a method of manufacturing the same. More particularly, the present invention relates to a honeycomb filter which excels in heat dispersion properties during heating and is effectively prevented from being damaged due to thermal stress, and a method of manufacturing the same.
2. Description of Related Art
Particulate matter and toxic substances contained in exhaust gas from an internal combustion engine, boiler, or the like must be removed from the exhaust gas taking the environmental effects into consideration. In particular, regulations concerning removal of particulate matter (hereinafter sometimes referred to as “PM”) discharged from a diesel engine have been tightened in Europe, USA, and Japan. Therefore, use of a honeycomb filter as a diesel particulate filter (hereinafter may be called “DPF”) for removing PM has attracted attention. The honeycomb filter has also been used to filter liquid such as service water or sewage.
As shown in FIG. 15, a honeycomb filter generally includes a cylindrical honeycomb structure 22 including a plurality of cells 24 which are partitioned by porous partition walls 23 in a honeycomb shape and function as fluid channels, and plugging members 27 disposed to alternately plug inflow openings 25 of predetermined cells 24a and outflow openings 26 of the remaining cells 24b. In a honeycomb filter 21 having such a configuration, a fluid such as gas or liquid flows into the cell 24 from the inflow opening 25 which is open without being plugged by the plugging member 27, and is discharged from the adjacent cell 24, specifically, the cell 24 which is plugged on the inflow opening 25 and is open on the outflow opening 26 through the porous partition wall 23. In this case, the partition wall 23 substantially functions as a filter, and carbon particulate matter or the like (hereinafter sometimes this expression is also referred to as PM) discharged from a diesel engine is deposited on the partition wall 23. Such a honeycomb filter 21 has a problem in which the temperature distribution inside the honeycomb structure 22 becomes uneven due to a rapid temperature change or localized heating caused by the exhaust gas, whereby cracks occur in the honeycomb structure 22. In the case of using the honeycomb filter as a DPF, it is necessary to regenerate the honeycomb filter by burning and removing the deposited carbon particulate matter. In this case, since a localized increase in temperature inevitably occurs, a high thermal stress easily occurs, whereby the honeycomb filter is damaged.
To deal with this problem, a method of dividing a honeycomb structure into a plurality of segments and bonding the segments using a bonding material (see Japanese Examined Patent Publication No. 61-51240, for example), and a honeycomb structure in which a channel separator is formed (see Japanese Patent Application Laid-open No. 2003-161136, for example) have been proposed.
It is effective to integrate the segments as in the method proposed in Japanese Examined Patent Publication No. 61-51240 in order to prevent a localized increase in temperature. However, since the step of manufacturing a number of segments and the step of integrating the segments are necessary for manufacturing one honeycomb structure, such a method is disadvantageous from the viewpoint of cost. The honeycomb structure proposed in Japanese Patent Application Laid-open No. 2003-161136 exhibits an insufficient effect of preventing damage caused by thermal stress. In particular, an increase in temperature may not be prevented or an increase in pressure loss may occur depending on the ratio of the channel separators formed. Therefore, room for further improvement remains.